This article, entitled Metal Detector (Turn your iPhone into a metal detector) comes from Karla Andrew and partner site Tech Ed 4 Kids
I am a SAHM/WAHM of three boys ranging in age from 3 to 18. We are working on saving enough for college at the same time as affording diapers. I author a few blogs, including http://teched4kids.com. I currently teach computer information technology classes for the local university and have in the past taught workshops for kid's in technology education besides being the Kentucky State FIRST LEGO League Championship Coordinator from 2005 to 2008.
Can’t find a metal object? This iPhone app uses the built in compass to find metal objects (reading the interference). It’s not really perfect, but for a home experiment it would be great to play with. You can even try to play "metal or not"! Or try a treasure hunt in your back yard….
How does it work? It seems like it can detect from a distance, but it’s much more accurate up close. To work the metal has to be magnetic e.g. steal, iron, etc.not aluminum. You can also try increasing the sensitivity to see if that helps it find treasure.
This is one app that can be fun to play with, and did I mention it’s free! It’s definitely worth giving it a try and it can be fun to experiment with different metals to see whats magnetic. Metal Detectors work by detecting an interference in the magnetic field of the earth. It’s also interesting that a compass won’t be accurate around a large amount of metal. I’m going to have to play with it later! Then on to a treasure hunt with the kids.